1. Field of the Invention
The present invention relates to a semiconductor device and, more particularlly, to a semiconductor device having a cross wire structure, as well as to a method for its manufacture.
2. Description of the Prior Art
In the art of semiconductor devices, particularly in the art of semiconductor integrated circuit devices, there has been a need to enhance the degree of circuit integration. However, with respect to the MIS type semiconductor memory device comprising a basic metal-insulator-semiconductor element, there is also a great need to enhance the memory capacity in addition to the degree of circuit integration. It is therefore necessary to increase the density of the MIS type semiconductor elements formed on the semiconductor substrate and, in turn, the density of the wiring formed over the substrate. As a result, more intersecting wires are formed on the substrate.
A so-called cross-over structure or cross-under structure was previously employed for producing the cross wire structure. According to the cross-over structure, an intermediate insulating layer is positioned between the two cross wires, one of which is elongated on the insulating layer as the upper wire layer.
According to the cross under structure, one of the cross wires is discontinued between two points and connected to an impurity diffusion region or to a buried diffusion region in the semiconductor substrate for connection between these two points and an elongated conducting line is thus produced. However, since the steps for producing the intermediate layer in the cross-over structure for insulating the upper and lower wire layers, as well as the steps for producing the upper wire layer, are indispensable to the overall process, the number of production steps is thus increased. As to the cross-under structure, it is indispensable to form on or in the substrate a diffusion layer for the lower wire, which makes it difficult to increase the degree of integration of the MIS semiconductor devices in the same substrate.